1. Field of Invention
The present invention relates to a pipe closure. More particularly, the present invention relates to a closure device that is insertable into a circular pipe, and which radially expands in response to mechanically induced axial contraction so as to effect a seal between the device and the inside wall of the pipe.
2. Description of the Prior Art
The present invention is particularly well adapted to be used as a test plug to close the open end of a submerged pipe for the pressure testing thereof, and for isolation of the pipe and and radioactive water. In the nuclear power industry, nuclear reactors typically comprise large diameter; vertically upright reactor vessels served by a plurality of (perhaps three or four) steam pipe lines which terminate at, and radially extend outboard from the wall of the reactor vessel. These substantially horizontal steam pipe lines each are provided with a closure valve which is intended to maintain a water-tight seal at pressures up to 60 psi. When shut down (i.e. for repair, maintenance, etc), the entire reactor vessel is flooded with water to shield radiation, with the entrance to the steam pipes in the wall of the reaction vessel being typically 40 feet beneath the surface of the water. The water over the radioactive fuel acts as a shield from radiation to the maintenance workers above the water.
It is desirable to periodically repair and pressure test the steam pipe closure valves. In order to repair a steam valve, the pug is inserted in the pipe line, and the pipeline downstream of the plug is draind. The steam valve is then repaired and tested by insertinserting a second valve, (a "test plug"), into the entrance to the steam pipe at the wall of the reactor vessel so as to isolate a section of the steam pipe between the "test plug" and the steam pipe closure valve, then close the "test plug" and pressurize the isolated section of the pipe. After the pressure test is completed, it is desirable to remove the "test plug" from the steam pipe. It is desirable that the insertion and removal of the test plug be accomplished remotely, that is: from above the surface of the water in reactor vessel, and, in particular, without requiring that any personnel be immersed or otherwise submerged in the water because draining down or the reactor to insert the plug manually would expose worker to harmful radiation levels.
Many prior removable pipe plugs are known which isolate sections of pipe and which have been used in the past as test plugs. Three general classifications of such prior are known. The first general classification of prior removable pipe plugs includes devices comprising an inflatable seal which engages the pipe wall when the inflatable seal is pressurized, (for example; U.S. Pat. No. 4,250,926). The second type of prior removable pipe plugs includes devices comprising an elastomeric seal which nominally fits inside of the pipe, but which radially expands to engage the wall of the pipe when the axial ends of the device are longitudinally drawn towards each other by mechanical means. Prior pipe plug devices of the third general classification include elastomeric seals configured in a "fail safe" construction such that the elastomeric seal always engages the pipe wall, except when the device is mechanically elongated axially so as to cause the elastomeric seal to radially contract, (for examples U.S. Pat. No. 5,119,861).
A problem of these prior pipe plug devices is that, because of the relatively low dimensional clearance between the sealing member and the inside wall of the pipe, such devices are not well suited for remote insertion into pipes, such as by robotic arms and the like.
Another problem of these prior pipe plug devices is that when they are constructed to have sufficient clearance between the sealing member and the inside of the pipe wall to facilitate remote insertion of the plug into the end of a pipe, such plugs typically don't have sufficient radial movement to effectively seal against high pressures. Those prior pipe plugs which retract to sufficiently small diameters for remote insertion into pipes, and which have sufficient radial-expansion capabilities to engage the interior pipe wall, typically rely upon an inflatable seal member to provide not only the seal between the device and the pipe but also the frictional force to restrain the device from being axially displaced along the pipe wall.
Another problem of such prior pipe plugs is that once the plug has initially inserted into a test pipe, the sealing member is typically induced to engage the wall of the pipe by one end of the plug being fixed while an opposite end is drawn toward it, thus causing one end of the sealing member to axial move while its opposite end remains stationary. Such axial movement of only one end of the sealing member typically causes the periphery of the sealing member to axially move along the pipe wall as the device is being "tightened", which movement may damage the sealing member.
Another problem with many prior pipe plugs is that once they are left in place for an extended period of time, they may become stuck inside of the pipe and difficult to remove, particularly from remote locations.
Another problem with prior pipe plugs is that it is extremely difficult, if not possible, to determine from a remote location whether or not the plug has properly closed against the pipe wall, (or whether or not the plug has properly released the pipe wall during plug removal operations), without conducting pressure tests on the plug.
Some prior pipe plug devices rely upon air driven equipment integrally constructed to the device to effect a torquing of axially threaded member so as to effect either the longitudinal contraction or extension of the device so as to cause an elastomeric member to either engage or disengage the pipe wall, respectively. In the event of failure of such air driven equipment, is it is difficult, if not virtually impossible, to replace or repair such equipment from a remote location.
Some prior pipe plugs require a constant source of air pressure in order to maintain a seal. In the event of failure or loww of the air supply, the seal in such prior devices is broken.
Another problem with prior pipe plug devices is that in many cases those plugs which are adapted to seal and restrain against hydrostatic pressure from one side of the plug are not equally well adapted to seal and restrain against hydrostatic pressure from the other side of the plug.